Apparatus and method for treating tumors near the surface of an organ

ABSTRACT

A system for treating a target region in tissue beneath a tissue surface comprises a probe for deploying an electrode array within the tissue and a surface electrode for engaging the tissue surface above the treatment site. Preferably, surface electrode includes a plurality of tissue-penetrating elements which advance into the tissue, and the surface electrode is removably attachable to the probe. The tissue may be treated in a monopolar fashion where the electrode array and surface electrode are attached to a common pole on an electrode surgical power supply and powered simultaneously or successively, or in a bipolar fashion where the electrode array and surface electrode are attached to opposite poles of the power supply. The systems are particularly useful for treating tumors and other tissue treatment regions which lie near the surface.

This application is a divisional of and claims the benefit of U.S.application Ser. No. 09/124,152, filed Jul. 28, 1998, now U.S. Pat. No.6,212,433 the disclosure of which is incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the structure and use ofradio frequency electrosurgical apparatus for the treatment of solidtissue. More particularly, the present invention relates to anelectrosurgical system having pairs of electrodes and electrode arrayswhich are deployed to treat large volumes of tissue, particularly forthe treatment of tumors which lie close to the surface of an organ.

The delivery of radio frequency energy to target regions within solidtissue is known for a variety of purposes. Of particular interest to thepresent invention, radio frequency energy may be delivered to diseasedregions in target tissue for the purpose of causing tissue necrosis. Forexample, the liver is a common depository for metastases of many primarycancers, such as cancers of the stomach, bowel, pancreas, kidney, andlung. Electrosurgical probes or deploying multiple electrodes have beendesigned for the treatment and necrosis of tumors in the liver and othersolid tissues. See, for example, the LeVeen™ Needle Electrode availablefrom RadioTherapeutics Corporation which is constructed generally inaccord with published PCT application WO 96/29946.

The probes described in WO 96/29946 comprise a number of independentwire electrodes which are extended into tissue from the distal end of acannula. The wire electrodes may then be energized in a monopolar orbipolar fashion to heat and necrose tissue within a defined volumetricregion of target tissue. In order to assure that the target tissue isadequately treated and to limit damage to adjacent healthy tissues, itis desirable that the array formed by the wire electrodes within thetissue be precisely and uniformly defined. In particular, it isdesirable that the independent wire electrodes be evenly andsymmetrically spaced-apart so that heat is generated uniformly withinthe desired target tissue volume. Such uniform placement of the wireelectrodes is difficult to achieve when the target tissue volume hasnon-uniform characteristics, such as density, tissue type, structure,and other discontinuities which could deflect the path of a wire as itis advanced through the tissue.

Of particular interest to the present invention, as recognized by theinventor herein, difficulties have arisen in using the multipleelectrode arrangements of WO 96/29946 in treating tumors which lay at ornear the surface of an organ, such as the liver. As illustrated in FIG.1, a LeVeen™ Needle Electrode used for treating a tumor T near thesurface S of a liver L can result in at least some of the tips ofelectrodes 12 emerging from the surface. Such exposure of the needletips outside of the liver is disadvantageous in a number of respects.First, the presence of active electrodes outside of the confinement ofthe organ being treated subjects other tissue structures of the patientas well as the treating personnel to risk of accidental contact with theelectrodes. Moreover, the presence of all or portions of particularelectrodes outside of the tissue being treated can interfere with properheating of the tissue and control of the power supply driving theelectrodes. While it would be possible to further penetrate the needleelectrode 10 into the liver tissue, such placement can damage excessiveamounts of healthy liver. Moreover, the heating characteristics of theliver tissue near the surface will be different from those of livertissue away from the surface, rendering proper treatment of the tumortissue near the surface difficult even if the electrodes are not exposedabove the surface.

For all of these reasons, it would be desirable to provide Improvedelectrosurglcal methods and systems for treating tumors which lie at ornear the surface of an organ or tissue mass. It would be particularlydesirable if such methods and systems could lesser the risk ofaccidental exposure of the treating electrodes above the tissue surface.It would be further desirable if the methods and systems would enhanceuniform treatment of the entire tumor mass, including those portionswhich lie near the surface of the organ being treated. Still further, itwould be desirable if the methods and systems could achieve treatment ofirregularly shaped tumors and tumors which extend from an organ surfaceto relatively deep within the organ. At least some of these objectiveswill be met by the invention of the present application.

2. Description of the Background Art

WO 96/29946 describes an electrosurgical probe having deployableelectrode elements of the type described above. The LeVeen™ NeedleElectrode constructed in accordance with the teachings of WO 96/229946is available from RadioTherapeutics Corporation, assignee of the presentapplication, and is illustrated in brochure RTC 002 published in 1998.Other electrosurgical devices having deployable electrodes are describedin German Patent 2124684 (Stadelmayr); U.S. Pat. Nos. 5,472,441 (Edwardset al.); 5,536,267 (Edwards et al.); and 5,728,143 (Gough et al.); andPCT Publications WO 97/06739; WO 97/06740; WO 97/06855; and WO 97/06857.Medical electrodes having pins and other structures are shown in U.S.Pat. Nos. 3,991,770; Re. 32,066; 4,016,886; 4,140,130; 4,186,729;4,448,198; 4,651,734; and 4,969,468. A skin surface treatment electrodefor the removal of blemishes having a circular array oftissue-penetrating pins is described in Rockwell, The Medical andsurgical Uses of Electricity, E.B. Trent & Co., New York, 1903, at page558.

SUMMARY OF THE INVENTION

The present invention provides improved methods, systems, and kits forperforming electrosurgical treatment of tumors and other diseaseconditions within body organs and other tissue masses. The methods,systems, and kits are particularly useful for treating tumors which lieat or near the surface of an organ, such as the liver, kidney, pancreas,stomach, spleen, particularly the liver. The present invention relies onapplying electrical energy, such as radio frequency or other highfrequency energy, to or between an internal tissue site and an externaltissue site on the surface of the organ. The energy may be applied in amonopolar fashion where the internal and external sites are maintainedat the same polarity and a dispersive or passive electrode disposed onthe patient's skin is maintained at the opposite polarity. The highfrequency energy can be applied simultaneously to both the internal andexternal sites, but will more usually be applied sequentially to onesite and then to the other. The energy may also be applied in a bipolarfashion where the internal treatment site is maintained at one polarityand the external treatment site maintained at the opposite polarity.Monopolar treatment is advantageous in permitting formation of two fullyformed lesions (necrosed regions) that can be overlapped to treat adesired region, but is disadvantageous since it requires use of adispersive electrode. Bipolar treatment eliminates the need for adispersive electrode and, by proper spacing, permits formation of asingle, continuous lesion. Such approaches reduce the risk of passinginternally deployed electrode(s) out through the surface of the bodyorgan and enhances the uniform electrosurgical treatment of tissuebetween the internal and exterior treatment sites.

A method according to the present invention for treating a target regionbeneath a tissue surface, such as a tumor site closely beneath thesurface of an organ, comprises deploying a first array of electrodes inthe tissue at or near the target region, preferably being distal to thesite. A second electrode is deployed on the tissue surface over thetarget region, and an electrical current, typically radio or other highfrequency current, is then applied to the tissues through theelectrodes. The current may be applied in a monopolar fashion, i.e. withthe first array of electrodes and the second electrode beingsimultaneously and/or successively connected to one pole of a powersource and a dispersive or passive electrode disposed on he patient'souter skin attached to the other pole. Alternatively, the first array ofelectrodes and the second electrode may be powered in a bipolar fashionby attaching them to opposite poles of the power supply.

The first array of electrodes is preferably deployed by positioning aprobe so that a portion of the probe lies near the target region in thetissue to be treated. A plurality of at least three array electrodes isthen advanced radially outwardly from the probe to define the firstelectrode array. The probe may be advanced directly into tissue, e.g.using a sharpened distal tip on the probe itself, or may be introducedtogether with a stylet which is then removed in order to permitintroduction of the electrodes through the probe. Conveniently, theprobe for deploying the electrode array may be constructed similarly oridentically to a LeVeena™ Needle Electrode as described in WO 96/29946.With such LeVeen™ Needle Electrodes, the electrodes advance initially inthe forward direction and then evert (i.e. follow an arcuate path fromthe tip of the probe) outwardly as they are further advanced into thetissue. The electrodes will preferably deploy outwardly to span a radiusof from 0.5 cm to 3 cm when the individual electrode elements are fullyextended. The array electrodes may be deployed at a depth below thetissue surface in the range from 2 cm to 10 cm, preferably from 3 cm to5 cm, (based on the position of the probe tip), with all individualelectrode elements preferably lying completely within tissue.

The second electrode may comprise a plate or other electrode structurewhich is engaged directly against the tissue surface. The plate or otherstructure will usually have an active electrode area in the range from 3cm² to 15 cm², preferably from 5 cm² to 10 cm². The second electrode mayfurther comprise a plurality of tissue-penetrating electrode elementswhich penetrate into the tissue when the second electrode is engagedagainst the tissue surface. The tissue-penetrating electrode elementswill usually be distributed over an area as set forth above for theplate electrode, and will preferably be capable of being penetrated to adepth below the tissue surface in the range from 3 mm to 10 mm,preferably from 4 mm to 6 mm. The tissue-penetrating elements willusually be parallel to each other, more usually being normal orperpendicular to a planar support plate, and are preferably pins havinga diameter in the range from 1 mm to 3 mm, preferably from 1.5 mm to 2mm, and a length sufficient to provide the tissue penetration depths setforth above. Optionally, the second electrode can be attached to theprobe after the first electrode array has been advanced and deployedbeneath the tissue. By attaching the second electrode to the probe, theentire system can be immobilized while the target region is beingtreated.

The active electrode area of both the first electrode array and secondelectrode will be the surface area of the electrode structure which isexpected to come into contact with tissue in order to transferelectrical current. The total active electrode area of the first arrayof electrodes will typically be in the range from 1 cm² to 5 cm²,preferably from 2 cm² to 4 cm². The area for the exemplary LeVeen™Needle electrode is about 3 cm². The active electrode area for thesecond electrode will be in the ranges generally set forth above. In thecase of second electrodes having pins projecting from the surface of aplate, the active electrode area may be defined by the pins, the platesurface, or a combination of both. it will be appreciated that portionsof the plate and/or the pins may be covered with electrical and thermalinsulation to achieve desired tissue treatment patterns. Portions of thefirst array of electrodes may also be insulated in order to change theelectrical transfer characteristics. For monopolar operation, there isgenerally no requirement that the electrode areas of the first electrodearray and the second electrode be the same. In the case of bipolaroperation, however, it will generally be desirable that the totalelectrode areas of both the first array of electrodes and the secondelectrode be generally the same, usually differing by no more than 20%,preferably differing by no more than 10%.

In an alternative method according to the present invention, control ofheat-mediated necrosis of a target region in tissue may be improved byinhibiting blood flow into the target region prior to the heattreatment. Large volume ablation and necrosis of highly vascularizedtissue, such as liver tissue, can be difficult because of thermaltransport from the region due to local blood flow. That is, blood flowthrough the tissue carries heat away. Moreover, because the degree ofvascularization in any particular region is unpredictable, the totalamount of heat which must be delivered in order to effectively necrosethe tissue is difficult to predict. Heat-mediated tissue necrosis maythus be improved by inhibiting blood flow into the treatment regionprior to heating. In some instances, it may be possible to tie off orclamp blood vessels(s) going into the region. Other known techniques forinhibiting blood flow and consequent heat loss include lowering bloodpressure to reduce blood flow in all regions of the body. For thermaltreatment according to the present invention, however, it will bepreferred to first necrose tissue at or near a distal periphery of thetarget region so that the vasculature is at least partly destroyed inorder to reduce the blood flow into the and/or the target region. Mostpreferably, this two-step method will be achieved using the first arrayof electrodes and second electrode as generally described above, wherethe second electrode is first energized to necrose tissue at or near theperiphery of the target region. While this approach is presentlypreferred, it will be appreciated that other heating modalities couldalso be employed, such as microwave heating, dispersed laser energyheating, electrical resistance heating, introduction of heated fluids,and the like.

In a still separate aspect of the methods of the present invention,deployment of the first electrode array and second electrode in a mannersuch that tissue is compressed therebetween will (after deployment) alsoinhibit blood flow into and from the target region between theelectrodes. Thus, the step of inhibiting blood flow may be achieved assimply as compressing the tissue in order to reduce blood flow throughthe target region between the electrodes. Preferably, such compressionis achieved using treatment electrodes which are also used forintroducing a frequency or other electrical current into the treatmentregion to effect the heating.

Systems according to the present invention for treating a target regionin tissue beneath the tissue surface comprise a probe having a distalend adapted to be positioned beneath the tissue surface and within orjust proximal to a target region in the tissue. A plurality ofelectrodes are deployable from the distal end of the probe to span aregion of tissue proximate the target region, usually just distal to thesite. The system further includes a surface electrode adapted to span anarea of the tissue surface over the target region. Preferably, thetissue electrode comprises a support having an electrode face and aninsulated face opposite to the electrode face. In the first embodiment,the electrode face may be generally flat and have an area in the rangesset forth above. Alternatively, the surface electrode may comprise aplurality of tissue-penetrating elements on the face of a plate or othersupport structure, typically from four tissue-penetrating elements tosixteen tissue-penetrating elements, more preferably from sixtissue-penetrating elements to nine tissue-penetrating elements.Optionally, the tissue-penetrating elements may be arranged in acircular or other pattern on the electrode face, further optionally withadditional electrodes interior to the peripheral electrodes. Thetissue-penetrating elements preferably comprise pins having the sizesdescribed above.

The surface electrode may optionally be connected to the probe using aconnector. Usually, the connector will attach the surface electrode in agenerally transverse orientation relative to the axis of the probe.Optionally, the connector can be flexible or in the form of a “universaljoint” which permits the surface electrode to align itself with thetissue surface even when the probe is entering at an angle relative tothe tissue surface which is not perpendicular.

The surface electrode and the probe may be electrically isolated fromeach other or may be electrically coupled to a common pole for monopolaroperation. For simultaneous monopolar operation, the surface electrode(and any tissue-penetrating elements thereon) will be electricallycoupled to the deployable electrode array on the probe so that all ofthe electrodes in the system can be connected to one pole of anelectrode surgical power supply. Alternatively, the array electrodes onthe probe may be electrically isolated from the second electrode and anytissue-penetrating elements thereon. When electrically isolated, theelectrode array and surface electrode can be driven separately (one at atime) in a monopolar fashion or simultaneously in a bipolar fashion,i.e. each connected to the opposite pole of an electrosurgical powersupply.

The probe will usually comprise a cannula having a proximal end, adistal end, and a lumen extending to at least the distal end. Thedeployable electrodes are resilient and disposed within the cannulalumen to reciprocate between a proximally retracted position where allelectrodes are radially constrained within the lumen and the distallyextended where all electrodes deploy radially outwardly. Usually, theelectrodes will have a shape memory which will deflect the electrodesradially outwardly as they extend from the cannula. The most preferredconfiguration for the deployable electrodes is arcuate so that theyassume an outwardly everted configuration as they are extended from thecannula. Usually, the array electrodes are connected to a rod structurewhich is reciprocatably received in the cannula lumen. Optionally, astylet may be provided as part of the system for placement in thecannula so that a sharpened tip of the cannula extends beyond the distaltip of the cannula. The cannula and stylet may then be introduced to thetarget region through tissue, after which the stylet is removed leavingthe lumen for receiving the electrode array. Usually, the cannula willhave a length In the range from 5 cm to 30 cm, preferably from 12 cm to20 cm, and an outer diameter in the range from 1 mm to 5 mm, usuallyfrom 1.5 mm to 2 mm. The electrode array will deploy outwardly to aradius in the range from 0.5 cm to 3 cm, preferably from 1 cm to 2 cmwhen fully extended. The electrode array will include at least 5electrodes, preferably including at least 8 electrodes and oftenincluding 10 or more electrodes.

Kits according to the present invention will comprise at least a secondelectrode, together with instructions for use for deploying an electrodearray in tissue and engaging the second electrode on a tissue surfaceabove the deployed electrode array for treating a tumor or other diseasecondition at or near the tissue surface. Usually, the second electrode(optionally together with a first electrode array) will be packaged in aconventional medical device package, such as a tray, box, tube, pouch,or the like. The instructions for use may be provided on a separatesheet of paper or may be printed in whole or in part on a portion of thepackaging.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates deployment of the prior art LeVeen™ Needle Electrodearray for treatment of a tumor region near the surface of a liver, withseveral of the electrode tips being shown exposed.

FIG. 2 illustrates and improved system according to the presentinvention comprising deployable electrode array, such as the LeVeen™Needle Electrode, in combination with a surface electrode assembly.

FIG. 3 is a detailed illustration of the distal end of the electrodearray of FIG. 2, shown with the electrode array fully deployed.

FIG. 4 is a side, cross-sectional view of the surface electrode that thesystem of FIG. 2.

FIG. 5 is a bottom view of the surface electrode of the system of FIG.2.

FIGS. 6A-6C illustrates the system of FIG. 2 being used for treatment ofa surface tumor in a monopolar configuration.

FIG. 7 illustrates the system of FIG. 2 connected for treatment of asurface tumor in a bipolar configuration.

FIG. 8 illustrates a kit according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Systems according to the present invention are designed to positionelectrode elements and assemblies within and over a treatment regionwithin solid tissue of a patient. The treatment region may be locatedanywhere in the body where hyperthermic exposure may be beneficial. Mostcommonly, the treatment region will comprise a solid tumor within anorgan of the body, such as the liver, kidney, pancreas, breast, prostate(not accessed via the urethra), and the like. The volume to be treatedwill depend on the size of the tumor or other lesion, typically having atotal volume from 1 cm³ to 150 cm³, usually from 1 cm³ to 50 cm³, andoften from 2 cm³ to 35 cm³. The peripheral dimensions of the treatmentregion may be regular, e.g. spherical or ellipsoidal, but will moreusually be irregular. The treatment region may be identified usingconventional imaging techniques capable of elucidating a target tissue,e.g. tumor tissue, such as ultrasonic scanning, magnetic resonanceimaging (MRI), computer-assisted tomography (CAT), fluoroscopy, nuclearscanning (using radiolabeled tumor-specific probes), and the like.Preferred is the use of high resolution ultrasound which can be employedto monitor the size and location of the tumor or other lesion beingtreated, either intraoperatively or externally.

Of particular interest to the present invention, tumors and othertreatment regions which lie at or near the surface of a body organ orother tissue mass may be effectively treated by deploying a first arrayof electrodes in the tissue at or within the target region, typicallybeing positioned at the posterior periphery of the region to be treated,and deploying a second electrode on the tissue surface over the targetregion. The second electrode may be a generally planar electrode butwill preferably comprise a plurality of tissue-penetrating electrodeelements which can penetrate through the tissue surface to provideeffective electrical coupling and current distribution to the tissuebeing treated. By then applying electrical current, usually radio orother high frequency current, to the tissue through the first array ofelectrodes and the second electrode, sequentially or simultaneously, thetissue can be effectively treated both at or near the surface as well asat lower depths within the tissue region.

Systems according to the present invention will usually comprise of aprobe having a distal end adapted to be positioned beneath the tissuesurface at or near the target region or region. A plurality oftissue-penetrating electrodes, typically in the form of sharpened, smalldiameter metal elements are reciprocatably attached to the probe so thatthey penetrate into tissue as they are advanced from a target regionwithin the target region, as described in more detail hereinafter. Theprimary requirement of such electrode elements is that they can bedeployed in an array, preferably a three-dimensional array, emanatinggenerally from a target region within the treatment region of thetissue. In the exemplary embodiment, the electrode elements are firstintroduced to the target region in a radially collapsed or otherconstrained configuration, and thereafter advanced into the tissue froma delivery cannula or other element in a divergent pattern to achievethe desired three-dimensional array. The electrode elements will divergeradially outwardly from the delivery cannula (located at the targetregion) in a uniform pattern, i.e. with the spacing between adjacentelectrodes diverging in a substantially uniform and/or symmetricpattern. Preferably, pairs of adjacent electrodes will be spaced-apartfrom each other in similar or identical, repeated patterns and willusually be symmetrically positioned about an axis of the deliveryelement. The electrode elements may extend or project along generallystraight lines from the target region, but will more usually be shapedto curve radially outwardly and optionally to evert proximally so thatthey face Partially or fully in the proximal direction when fullydeployed. It will be appreciated that a wide variety of particularpatterns can be provided to uniformly cover the region to be treated.

The second electrode, also referred to herein as the surface electrode,is intended to provide electrical contact with a region of the tissuesurface which is located generally over the target region with thetissue. When the tumor or other target region extends to the tissuesurface, the second electrode will preferably be positioned to cover allor as much of the exposed tumor as possible. In Its simplest form, thesecond electrode may be a generally flat or planar plate electrode, e.g.being a simple disc having a an area within the ranges set forthpreviously. Preferably, however, the second electrode will comprise aplurality of tissue-penetrating electrode elements which projectperpendicularly from the electrode plate or other support structure. Thetissue-penetrating electrode elements will form part of the electricallyconductive electrode structure, with the supporting plate or otherstructure being either active or inactive, i.e. the rest of thesupporting structure may be insulated so that it is not electricallyactive when in contact with tissue. In almost all cases, the oppositeface of the electrode structure, i.e. all portions of the electrodewhich are not intended to contact tissue, will be electrically andthermally insulated to prevent accident tissue contact with electricallyactive and heated components of the electrode during performance of aprocedure. The tissue-penetrating elements may be simple blunt pins,sharpened pins, or needles which project perpendicularly from the planarelectrode support, usually having dimensions within the ranges set forthabove. The number of tissue-penetrating elements on the second electrodewill also be within the ranges set forth above. The electricallyconductive components of the second electrode, including all those whichcome into contact with tissue, will usually be formed from or platedwith an electrically conductive metal, such as stainless steel, gold,silver, brass, and the like.

The second electrode will preferably be attachable to the probe whichdeploys the first electrode array, usually being attached after thefirst electrode array is deployed. In the exemplary embodiment, thesecond electrode is a disc structure having a central aperture which canbe selectively and slidably positioned over the probe shaft and lockedinto position. In such cases, the second electrode will be disposed in agenerally transverse orientation when the electrode is locked on theprobe. When the second electrode carries tissue-penetrating elements,those elements will usually be aligned in a parallel orientation withthe axis of the probe. In some cases, however, it may be desirable toattach the second electrode so that it is capable of pivoting orotherwise adjusting its planar orientation relative to the axis of theprobe. For example, the second electrode may be attached using aball-and-socket or other universal joint which permits relatively freemovement of the second electrode about the pivot point defined by theattachment to the probe. In the exemplary embodiments, if the tumorbeing treated approaches or reaches the surface of the tissue or organ,the second (surface) electrode may be placed onto the shaft of the probeafter the first electrode array is deployed. Deployment of the firstelectrode array will anchor the distal end of the probe in tissue,permitting the second electrode to be firmly engaged against the tissuesurface, preferably so that tissue between the deployed electrode arrayand the second electrode array and the second electrode will be slightlycompressed.

Such compression has at least two advantages. First, both electrodes areheld firmly in place so that they are less likely to become dislodged.More importantly, compression of the tissue tends to inhibit blood flowinto the treatment region rendering heating of the tissue more rapid andmore controllable. When employing tissue-penetrating elements on thesecond electrode, it is desirable that they be fully inserted into thetissue. The depth of tissue penetration by the elements largelydetermines the depth of the surface lesion being created, i.e. the morefully the elements penetrate into tissue, the deeper the lesion will be.

Monopolar operation may be effected in two ways. Most commonly, thefirst electrode array and second electrode will be electrically isolatedfrom each other and powered separately, preferably with the electrodearray being powered first in order to necrose tissue at a boundary ofthe target region and inhibit blood flow into the region. In othercases, however, if sufficient power is available, the first electrodearray and second electrode may be driven simultaneously while attachedto a common pole on an electrosurgical power supply. Although notessential, the first electrode array and second electrode may havesimilar available electrode areas, so that approximately the sameheating will occur from both the electrodes simultaneously, but at halfthe power level which will be achieved using the same power level withonly a single electrode.

For bipolar operation, the electrically conductive components of thesecond electrode will be electrically isolated from the electricallyconductive components of the first electrode array. In that way, thesecond electrode and first electrode array can be attached to oppositepoles of a radio frequency or other power supply in order to effectbipolar current flow between the deployed electrode components.Preferably, the available surface areas of the first electrode array andthe second electrode will be approximately equal so that heating (energytransfer into unit volumes of adjacent tissue) occurs at approximatelythe same rate from both electrode structures. If the areas differsignificantly from each other, the current flux from the smallerelectrode will be denser, leading to possible overheating of theadjacent tissue.

It will be appreciated that in monopolar operation, a passive ordispersive “electrode” must also be provided to complete the return pathfor the circuit being created. Such electrodes, which will usually beattached externally to the patient's skin, will have a much larger area,typically about 130 cm² for an adult, so that current flux issufficiently low to avoid significant heating and other biologicaleffects. It may also be possible to provide such a dispersive returnelectrode directly on a portion of a sheath, core element, or otherportion of the system of the present invention (generally, when thereturn electrode is on the same sheath or core, the device may still bereferred to as bipolar).

The RF power supply may be a conventional general purposeelectrosurgical power supply operating at a frequency in the range from300 kHz to 1.2 MHz, with a conventional sinusoidal or non-sinusoidalwave form. Such power supplies are available from many commercialsuppliers, such as Valleylab, Aspen, and Bovie. Most general purposeelectrosurgical power supplies, however, operate at higher voltages andpowers than would normally be necessary or suitable for the methods ofthe present invention. Thus, such power supplies will usually beoperated at the lower ends of their voltage and power capabilities. Moresuitable power supplies will be capable of supplying an ablation currentat a relatively low voltage, typically below 150V (peak-to-peak),usually being from 50V to 100V. Such low voltage operation permits useof a power supply that will significantly and passively reduce output inresponse to impedance changes in the target tissue. The power willusually be from 50W to 150W, usually having a sine wave form, but otherwave forms would also be acceptable. Power supplies capable of operatingwithin these ranges are available from commercial vendors, such asRadionics and RadioTherapeutics Corporation. A preferred power supply ismodel RF-2000, available from RadioTherapeutics Corporation, MountainView, Calif., assignee of the present application.

The probe which contains the deployable electrode elements will usuallybe contained by or within an elongate member, typically a rigid orsemi-rigid, metal or plastic cannula. In some cases, the cannula willhave a sharpened tip, e.g. be in the form of a needle, to facilitateintroduction to the tissue target region. In such cases, it is desirablethat the cannula or needle be sufficiently rigid, i.e. have sufficientcolumn strength, so that it can be accurately advanced through tissue.In other cases, the cannula may be introduced using an internal styletwhich is subsequently exchanged for the electrode array. In the lattercase, the cannula can se relatively flexible since the initial columnstrength will be provided by the stylet. The cannula serves to constrainthe individual electrode elements in a radially collapsed configurationto facilitate their introduction to the tissue target region. Theelectrode elements can then be deployed to their desired configuration,usually a three-dimensional configuration, by extending distal ends ofthe electrode elements from the distal end of the cannula into thetissue. In the preferred case of the tubular cannula, this can beaccomplished simply by advancing the distal ends of the electrodeelements distally from the tube so that they emerge and deflect (usuallyas a result of their own spring or shape memory) in a radially outwardpattern. Alternatively, some deflection element or mechanism could beprovided on the elongate member to deflect members with or without shapememory in a desired three-dimensional pattern.

Referring to FIGS. 2-5, an exemplary electrode deployment system 20constructed in accordance with the principles of the present invention.The system 20 comprises a probe 22 and a surface electrode 24. The probe22 will be generally as described above, and will preferably be aLeVeena™ Needle Electrode of the type which is available fromRadioTherapeutics Corp., Mountain View, Calif., assignee of the presentapplication. The probe 22 comprises a handle 26 and a cannula 28, wherethe cannula has a sharpened distal tip 30 which may be directlyintroduced through tissue to a target region. As best observed in FIG.3, a plurality of everting electrodes 32 may be deployed from the tip 30by advancing a button 34 on the handle. The everting electrodes 32 areelectrically coupled to a connector 40 (FIG. 2) at the proximal end ofthe handle 22 through a shaft 42 which is used to deploy the electrodes.The outer surface of the cannula 28 will be insulated so that currentflows only through the everted electrodes 32 and the surface electrode24.

As best observed in FIGS. 4 and 5, the surface electrode 24 comprises anelectrically conductive plate 50 having a plurality oftissue-penetrating pin electrodes 52 projecting forwardly from face 56thereof. Preferably, the pin electrodes 52 will project in a generallyperpendicular direction from the planar face 56. Usually, but notnecessarily, face 56 will be covered with an insulating layer so thatelectrical contact is made through only the pins 52. In some cases,however, it may be desirable to leave the face 56 uninsulated so thatelectrical contact can be made through the face as well. A slot 60 isformed in the plate 50 so that the surface electrode 24 may be mountedonto the cannula 28 as seen in FIG. 2. An enlarged central aperture 62may be provided for locking on to the cannula. Alternative lockingmechanisms may also be provided, such as compression locks, latches, andthe like (not illustrated) which permit axial movement of the surfaceelectrode 24 along the length of cannula 28 and selective locking of thesurface electrode at a desired position. Optionally, a collar 64 may beprovided on the opposite face 70 of the plate to assist in holdingand/or locking of the surface electrode 24 on the cannula 28.Preferably, electrical and thermal insulating layers 72 will be providedover all exposed portions of the surface electrode so that the chance ofaccidental contact between the surface electrode and other tissuestructures near the treatment region is minimized. It will beappreciated that the surface electrode 24 may be attached at virtuallyany axial location along the cannula 28 so that the distance between thesurface electrode and the distal tip (electrode deployment point) 30 ofthe probe 22 can be fully adjusted. Also, as described above, theconnection between the cannula 28 and the surface electrode 24 can bemade to freely pivot so that the electrode can adjust to differentsurface orientations of the tissue after the cannula 28 has beenintroduced into tissue.

Referring now to FIGS. 6A-6C, monopolar operation of the electrodesystem 20 will be described. After imaging the tumor or other treatmentregion T in the liver L, the cannula 28 is introduced through the tissuesurface F until the distal up 30 advances to point generally at theposterior of the tumor region T. The electrodes 32 are then deployed byadvancing them out of the distal tip 30, and the surface electrode 24placed on to the cannula 28. The surface electrode 24 is then advancedtoward the tissue surface S so that the electrode pins 52 advance intothe tissue, and more particularly into the treatment region T, asillustrated in FIG. 6A. Current may then be applied in either of the twogeneral modes described above. In a first mode (not illustrated) thesurface electrode 24 and deployed electrodes are powered simultaneouslyto treat the entire target region T at once. In the illustrated andpresently preferred mode, however, the deployed electrodes 32 are firstenergized to necrose a boundary region B1, as generally shown in FIG.6B. Necrosis of the boundary region B1 will not only treat a significantportion of the tissue within the target region T, it will also at leastpartially inhibit blood flow into and from the target region tofacilitate subsequent treatment with the surface electrode 24. After thefirst treatment step using deployed electrodes 32 is completed, thesurface electrode 24 will be separately powered in order to treat asecond boundary region B2 as shown in FIG. 6C. Preferably, these regionswill at least partially overlap, and more preferably will completelyoverlap in order to fully necrose the treatment region T.

Bipolar treatment according to the present invention is effected inmanner very similar to that described for monopolar treatment. As shownin FIG. 7, electrodes 32 and surface electrode 34 are deployed on eitherside of the treatment region T. The electrodes 32 and 24 will, however,be electrically isolated from each other. A first pole of the powersupply 100 is then coupled to the electrodes 32 of the interiorelectrode array while the second pole of the power supply is connectedto the surface electrode 24. Radio or other high frequency energy canthen be applied to the tissue in a bipolar fashion where current flowsbetween the electrodes 32 and surface electrode 24, with the currentflux being localized generally within the tumor or other treatmentregion T.

Referring now to FIG. 8, a kit according to the present invention willcomprise at least a surface electrode 24, optionally a probe 20, andinstructions for use IFU. The probe 20 and surface electrode 24 may begenerally as described above, and the instructions for use will setforth a method for employing the probe 20 and the surface electrode 24in accordance with any of the methods of the present invention describedabove. The instructions for use will generally be written on a packageinsert or other separate piece of paper 150, but may also be printed inwhole or in part on the packing materials. Usually, all components ofthe kit will be packaged together in a conventional package 160, such asa pouch, tray, box, tube, or the like. Preferably, all system componentswill be sterilized within the package so that they are immediately readyfor use in the sterile environment.

While the above is a complete description of the preferred embodimentsof the invention, various alternatives, modifications, and equivalentsmay be used. Therefore, the above description should not be taken aslimiting the scope of the invention which is defined by the appendedclaims.

What is claimed is:
 1. A system for treating a target region in tissuebeneath a tissue surface, said system comprising: a probe having adistal end adapted to be positioned beneath the tissue surface to a sitein the tissue; a plurality of electrodes deployable from the distal endof the probe to span a region of tissue proximate the target region; anda surface electrode removably attachable to the probe and adapted tospan an area of the tissue surface over the target region.
 2. A systemas in claim 1, wherein the surface electrode comprises a support havingan electrode face and an insulated face opposite to the electrode face.3. A system as in claim 2, wherein the electrode face is generally flat.4. A system as in claim 3, wherein the flat electrode face has an areain the range from 2 cm² to 10 cm².
 5. A system as in claim 2, whereinthe surface electrode comprises a plurality of tissue-penetratingelements on the electrode face.
 6. A system as in claim 5, wherein thesurface electrodes comprise from 4 to 16 tissue-penetrating elements. 7.A system as in claim 5, wherein the tissue-penetrating elements are pinshaving a diameter in the range from 1 mm to 3 mm and a depth from theelectrode face in the range from 3 mm to 10 mm.
 8. A system as in claim1, further comprising a connector on the surface electrode whichremovably attaches said electrode to the probe.
 9. A system as in claim1, further comprising a connector on the surface electrode which isselectively attachable at different axial positions along the probe. 10.A system as in claim 1, wherein the surface electrode is adapted tomechanically couple to the probe, wherein the plurality of electrodesand surface electrodes are electrically coupled for monopolar operation.11. A system as in claim 10, wherein the surface electrode iselectrically coupled to the plurality of electrodes when the surfaceelectrode is mounted on the probe.
 12. A system as in claim 10, whereinthe surface electrode is electrically isolated from the plurality ofelectrodes when the surface electrode is mounted on the probe.
 13. Asystem as in claim 1, wherein the surface electrode is adapted tomechanically couple to the probe, wherein the plurality of electrodesremain electrically isolated from the surface electrode for bipolaroperation.
 14. A system as in claim 1, wherein the probe comprises: acannula having a proximal end, a distal end, and a lumen extending to atleast the distal end, and wherein the plurality of electrodes areresilient and disposed in the cannula lumen to reciprocate between aproximally retracted position wherein all electrodes are radiallyconstrained within the lumen and a distally extended position whereinall electrodes deploy radially outwardly, said plurality including atleast three electrodes.
 15. A system as in claim 14, wherein at leastsome of the electrodes are shaped so that they assume an outwardlyeverted configuration as they are extended distally into tissue from thedistal end of the cannula.
 16. A system as in claim 14, furthercomprising a rod structure reciprocatably received in cannula lumen,wherein the electrodes are secured at a distal end of the rod in anequally spaced-apart pattern.
 17. A system as in claim 14, wherein thecannula has a tissue-penetrating member at its distal end to permitadvancement of the cannula through tissue.
 18. A system as in claim 14,further comprising a stylet reciprocatably received in the cannulalumen, wherein the stylet. may be used for initially positioning thecannula in tissue and thereafter exchanged with the electrodes.
 19. Asystem as in claim 14, wherein the cannula has a length in the rangefrom 5 cm to 30 cm and an outer diameter in the range from 1 mm to 5 mm.20. A system as in claim 14, wherein the electrodes deploy outwardly toa radius in the range from 0.5 cm to 3 cm when fully distally extendedfrom the cannula.
 21. A system as in claim 14, wherein the pluralityincludes at least five electrodes.
 22. A system as in claim 14, whereinthe plurality includes at least eight electrodes.
 23. A system as inclaim 14, wherein the plurality includes at least ten electrodes.
 24. Asystem as in claim 1, wherein the active areas of the plurality ofelectrodes and the surface electrode are approximately equal and theplurality of electrodes and surface electrode are electrically isolated.25. A system for treating a target region in tissue beneath a tissuesurface, said system comprising: a probe having a distal end adapted tobe positioned beneath the tissue surface to a site in the tissue; aplurality of electrodes deployable from the distal end of the probe tospan a region of tissue proximate the target region; and a surfaceelectrode removably attachable to the probe and adapted to span an areaof the tissue surface over the target region, said surface electrodecomprising a plurality of tissue-penetrating elements.
 26. A system asin claim 25, wherein the surface electrode comprises a support having anelectrode face and an insulated face opposite to the electrode face,wherein the tissue-penetrating elements project from the electrode face.27. A system as in claim 26, wherein the electrode face is generallyflat.
 28. A system as in claim 27, wherein the flat electrode face hasan area in the range from 2 cm² to 10 cm².
 29. A system as in claim 28,wherein the tissue-penetrating elements project substantiallyperpendicularly from the electrode face.
 30. A system as in claim 29,wherein the surface electrodes comprise from 4 to 15 tissue-penetratingelements.
 31. A system as in claim 25, wherein the tissue-penetratingelements are pins having a diameter in the range from 1 mm to 3 mm and adepth from the electrode face in the range from 3 mm to 10 mm.
 32. Asystem as in claim 25, further comprising a connector on the surfaceelectrode which removably attaches said electrode to the probe.
 33. Asystem as in claim 25, further comprising a connector on the surfaceelectrode which is selectively attachable at different axial positionsalong the probe.
 34. A system as in claim 25, wherein the surfaceelectrode is adapted to mechanically couple to the probe, wherein theplurality of electrodes and surface electrodes are electrically coupledfor monopolar operation.
 35. A system as in claim 34, wherein thesurface electrode is electrically coupled to the plurality of electrodeswhen the surface electrode is mounted on the probe.
 36. A system as inclaim 34, wherein the surface electrode is electrically isolated fromthe plurality of electrodes when the surface electrode is mounted on theprobe.
 37. A system as in claim 34, wherein the surface electrode isadapted to mechanically couple to the probe, wherein the plurality ofelectrodes remain electrically isolated from the surface electrode forbipolar operation.
 38. A system as in claim 25, wherein the probecomprises: a cannula having a proximal end, a distal end, and a lumenextending to at least the distal end, and wherein the plurality ofelectrodes are resilient and disposed in the cannula lumen toreciprocate between a proximally retracted position wherein allelectrodes are radially constrained within the lumen and a distallyextended position wherein all electrodes deploy radially outwardly, saidplurality including at least three electrodes.
 39. A system as in claim38, wherein at least some of the electrodes are shaped so that theyassume an outwardly everted configuration as they are extended distallyinto tissue from the distal end of the cannula.
 40. A system as in claim38, further comprising a rod structure reciprocatably received incannula lumen, wherein the electrodes are secured at a distal end of therod in an equally spaced-apart pattern.
 41. A system as in claim 38,wherein the cannula has a tissue-penetrating member at its distal end topermit advancement of the cannula through tissue.
 42. A system as inclaim 38, further comprising a stylet reciprocatably received in thecannula lumen, wherein the stylet may be used for initially positioningthe cannula in tissue and thereafter exchanged with the electrodes. 43.A system as in claim 38, wherein the cannula has a length in the rangefrom 5 cm to 30 cm and an outer diameter in the range from 1 mm to 5 mm.44. A system as in claim 38, wherein the electrodes deploy outwardly toa radius in the range from 0.5 cm to 3 cm when fully distally extendedfrom the cannula.
 45. A system as in claim 38, wherein the pluralityincludes at least five electrodes.
 46. A system as in claim 38, whereinthe plurality includes at least eight electrodes.
 47. A system as inclaim 38, wherein the plurality includes at least ten electrodes.
 48. Asystem as in claim 25, wherein the active areas of the plurality ofelectrodes and the surface electrode are approximately equal and theplurality of electrodes and surface electrode are electrically isolated.